09272016Tue
Last updateTue, 27 Sep 2016 9pm

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Caution: Horizontal Stem Installation Ahead

Caution: Horizontal Stem Installation Ahead

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The Critical Stem Nut: Who is Responsible for Maintenance?

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An Alternative Basics Education: Valve Ed Comes to You!

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Give Your Flow Meter a Happy Home

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Wolseley Reports 2016 Full Year Results

1 HOUR AGO

Wolseley plc delivered an improvement in overall results for the fiscal year ending July 31, 2016, up 8.5% from last year. Revenue of $18.7 billion was 4.2% ahead at constant exchange rates and 2.4% ahead on a like-for-like basis. Price deflation, particularly in the U.S., reduced revenue by 1.5%. Imp...

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ValvTechnologies Joins MSS of the Valve and Fittings Industry Committee

5 HOURS AGO

ValvTechnologies, Inc. has been unanimously approved for membership in the Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry Committee. Representing ValvTechnologies is Tony Majka, director of engineering.

The MSS is a non-profit technical association organized for develo...

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Alaska, ConocoPhillips Forming LNG Joint Venture

1 DAY AGO

The State of Alaska, through the Alaska Gasline Development Corporation (AGDC), and ConocoPhillips Alaska Inc. have executed a Memorandum of Understanding regarding negotiations to form a joint venture (JV) that could facilitate marketing LNG from the Alaska LNG project to global LNG markets and acqui...

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Many Houston Chemical Facilities Could Be Operating Illegally

1 DAY AGO

“Firefighters once routinely visited buildings in their districts to plan for emergencies — including ferreting out hazmat sites — but those visits stopped in April 2014. The department had started entering old plans into a new, sophisticated database and didn't want to create a ba...

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U.S. Consumer Confidence Surges to Nine-Year High

6 HOURS AGO

The Conference Board Consumer Confidence Index, which had increased in August, improved further in September. The Index now stands at 104.1, up from 101.8 in August. The 104.1 figure is the highest since August 2007.

“Consumer confidence increased in September for a second consecutive month and i...

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Texas Manufacturing Strengthened in September

6 HOURS AGO

Texas factory activity increased markedly in September, according to business executives responding to the Texas Manufacturing Outlook Survey . The production index, a key measure of state manufacturing conditions, rose 12 points to 16.7, suggesting output picked up at a notably faster pace this month...

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A Case for Mechanical Temperature Control

vmwnt12_beyond_valves_fig1Instrument, mechanical or project engineers may see a multitude of temperature applications cross their desks. Their immediate reaction might be to employ a temperature control loop. But could a mechanical, self-operated temperature regulator be a better solution for the valve application?

When approaching a temperature control application, the engineer usually considers:

  • The degree of accuracy needed
  • Whether the application requires feedback (Are limit switches/output signals used?)
  • Whether the application needs to be controlled through a DCS, PLC or other type of controller
  • The budget for the application.

The answer to whether a mechanical temperature regulator might be a cost-effective and reliable solution for the application depends on those considerations.

In almost any process facility, a variety of temperature control applications can be found. As with any controlled variable, both the accuracy and criticality of those applications can vary widely. Often, non-critical temperature applications become instrumented control loops even when a self-operated or mechanical regulator could provide the desired accuracy along with a substantial cost savings.


WHAT’S CONSIDERED

vmwnt12_beyond_valves_fig1Figure 1. Temperature regulatorA typical temperature control loop ­(Figure 1) requires:

  • a temperature sensor
  • wiring and conduit
  • connection to a controlling device
  • a control valve (and sometimes a positioner and/or I/P converter, and an air-filter regulator)
  • plant air

A self-contained temperature regulator requires no power, no air supply or other expensive compo­nents to operate. Representative costs based on a 1-inch line size would be:

  • Temperature transmitter: $300-1,000
  • Temperature controller: $400-1,000
  • Control valve and actuator: $1,500-3,000
  • I/P converter: $200-350
  • Air set regulator: $100-150
  • Positioner: $500-2,000
  • Control loop total: $3,000-7,500
  • Temperature regulator: $500-2,500

Although designs may vary from manufacturer to manufacturer, most temperature regulators operate on the same principle. A premeasured amount of “fill” is drawn into the thermal system filling the upper diaphragm chamber, the capillary tube and most of the bulb. As the controlled temperature increases, the fill in the sensing bulb begins to vaporize and creates pressure on the sealed system. This pressure drives the valve stem, closing direct-acting valves or opening reverse-acting valves. By using different fill fluids, many different temperature control ranges can be offered for both cooling and heating applications—temperature ranges are readily available from -20° F (-29° C) to 500° F (260° C).

Applications for which these devices might be ideal include tank farms, large heat exchangers, heat exchangers with slow temperature changes, area heating/cooling (warehouse/maintenance shops) and steam tracing.

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